The invention relates to an array substrate of a liquid crystal device and fabrication thereof, and in particular to a flat thin film transistor with high transmittance of an array substrate of a liquid crystal device and fabrication thereof.
Currently, Liquid crystal displays (LCD) are regarded as the mainstream among various flat panel displays. A working principle of the liquid crystal display is based on alignment orientation of liquid crystal molecules. Owing to dielectric anisotropy and conductive anisotropy of liquid crystal molecules, molecular orientation of liquid crystal molecules can be shifted under an external electronic field, such that various optical effects are produced. An LCD panel is generally made up of two substrates, with a certain gap preserved therebetween, and a liquid crystal layer filled in the gap. Respective electrodes are formed on the two substrates, respectively, to control the orientation and shift of liquid crystal molecules.
A conventional structure of a thin film transistor (TFT) used in a TFT flat display device is shown in FIG. 1, and its manufacturing process is described below. The substrate 10 has a TFT region, and a first metal layer is formed in the TFT region. The first metal layer is patterned to form a gate line 12 along a first direction by a first lithography and etching process. An insulating layer 14, a semiconductor layer 16, an n-doped silicon layer 18 and a second metal layer 20 are sequentially deposited over the gate line 12. The semiconductor layer 16 can be an amorphous silicon layer. A second lithography and etching process is used to pattern the amorphous silicon layer 16, the n-doped silicon layer 18 and the second metal layer 20 to expose the insulating layer 14. The second metal layer 20 is also patterned to form a signal line along a second direction, and the second direction is vertical to the first direction. The third lithography and etching processes are conducted to define a channel 19 between the second metal layer 20 and the n-doped silicon layer 18 so as to expose the amorphous silicon layer 16 in the channel 19. A source electrode and a drain electrode are formed and separated by the channel 19.
Due to a higher stack of the conventional TFT, orientations of liquid crystals around the thin film transistor are affected. In addition, the protruded thin film transistor also affects alignment of liquid crystals by rubbing. Further, multiple layers formed on pixels affect transmittance of a liquid crystal display panel, reducing brightness thereof.
Additionally, defects are easily formed at source electrodes and drain electrodes due to inadequate step coverage when forming the second metal layer 20. Shorts easily occur when sidewalls of the second metal layer are discontinuous, and layers thereunder are not well protected.